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Graphic element Research > Growth > Research projects > Products & processes projects > Ultra-fast lasers bring micromachining breakthroughs
Graphic element Ultra-fast lasers bring micromachining breakthroughs
    02-10-2000
 

In fields such as electronics, medical engineering and aerospace, femtosecond (fs = 1 x 10-15s) laser pulses could offer considerable advantages over conventional nanosecond lasers for high precision micro-machining of problematic and delicate materials. BRITE/EURAM project FEMTO, co-ordinated by Laser Zentrum Hannover (LZH), brings together researchers, equipment manufacturers and end users in a combined effort to design and test an easy-to-use system suitable for industrial application.

Precise Processing

Femtosecond laser machining enables a wide variety of materials - from metals, ceramics and glass, to heat-sensitive plastics - to be shaped with very high precision. The ultra-short duration of the high-energy pulses enables relatively high material removal rates to be achieved, with minimal thermal and mechanical damage. Processing is thus not only precise, but also more repeatable. To date, however, its use has been limited by the fact that the available equipment is bulky and complex.

LZH therefore sought to use its extensive experience of the technology in a research environment as a basis for developing a routine tool that would be of value to various sectors of European industry.

Its search for collaborators produced a consortium bringing together a wide range of relevant expertise. The partners include Thompson CSF-Laser, who at the start of the project were Europe's only supplier of femtosecond solid-state lasers (based on titanium-sapphire), and laser machine manufacturer Exitech. The University of Bordeaux's Equipe Laser Intense et Applications (ELIA) contributes further research capability, while medical implant maker Biotronik and Photek, a producer of specialised camera tubes and detectors, are both potential industrial users of the resultant technology.

The group was able to attract the necessary funding, and the three-year FEMTO project was launched in September 1998. This concentrated initially on studying the interaction of lasers with different types of material, using the available research-scale equipment. Promising applications were targeted in the domains of each of the two end-user partners.

Industrial applications

For Photek, the aim was to replace electro forming and Electro Discharge Machining (EDM) by laser ablation for the production of components such as the metal accelerator grids employed in photomultiplier tubes and other devices. By enabling the perforations to be reduced down to the micron scale, this would open the door to new applications, including detectors for ultra-fast electronic signal measuring instruments and fluorescence microscopy imaging.

So far, the machining of metals has proved to be rather slow and problematic - but LZH recently supplied a batch of apparently successful samples for evaluation by Photek. Trials will shortly commence.

Considerably greater progress has been made in the medical field - where Biotronik sought, in particular, to explore the manufacture of biodegradable stents for use in minimal invasive heart surgery. A stent is a slotted tube that is inserted into a blocked blood vessel after dilation, in order to prevent subsequent closure. To date, these have typically been manufactured in stainless steel or nickel-based shape-memory alloys. Quite often such support is required only for a period of some months, but the metal stent cannot be removed from the vessel at a later date. In some 20-30% of cases, however, its invasive nature actually provokes reblockage.

The FEMTO team has therefore been studying the use of biodegradable polymers. While work goes on to optimise the actual design, femtosecond laser technology has already proved to be a practical means of fabricating the stents. Around 100 of these have been produced to date. They are currently undergoing testing, both to assess the effect of the laser treatment on the material properties and to evaluate performance in terms of mechanical stability, degradation time and solubility. Some in situ experiments have been conducted with animals, but human trials remain some way off.

Compact machine designed

WAt the same time, the production of a prototype industrial machine is nearing completion. By developing a purpose-designed laser generator with significantly fewer parameter variation options than are necessary in a research system, Thompson CSF-Laser succeeded in reducing the dimensions down to an acceptable size. Working in parallel, Exitech has built an initial micro-machining station dedicated to manufacture of stents as well as grids. The two elements will be assembled and tested before the year-end. The complete unit will delivered to LZH early in 2001 to permit further optimisation and more extended trials. A finalised version is likely to be adopted for commercial production by the partners in eighteen months to two years.

Despite the initial problems in machining metals, Exitech considers that the technology also shows real promise for applications such as the manufacture of micromoulds and fuel injector nozzles, as well as burr-free drilling of printed circuit boards. LZH will also continue to experiment with other polymers. The consortium considers that its progress to date puts it significantly ahead of US rivals.

   
Precise processing
Industrial applications
Compact machine designed
   

Key data

Research targeting machine tools production under the Innovative products, processes and organisation key action goes beyond improvements in traditional machine tool-making. Rapid and high-precision laser technology is leading to the development of delicate materials for use in a variety of disciplines, including medical instruments for surgery.

Project: FEMTO - Precise machining by femtosecond laser pulses (BRPR980694)

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